Some myths just refuse to die. Such is the case with the persistent misinformation about cannabis being a “gateway” to other drugs; it isn’t true, but prohibitionists are still spreading the lie.

State tax collectors say that more than $230 million worth of legal marijuana was sold in Los Angeles County last year: LA is the most populous county in the country’s most populous state, so it stands to reason that it also has the most cannabis business of any place in California.

And it does — again, by a large measure.

Now that recreational cannabis is legal in California, Los Angeles will likely become the top destination for marijuana-seeking visitors to the state when sales begin sometime next year.

And why not? Go to Hollywood, walk around Venice Beach, and wrap up the afternoon at a weed dispensary. Just look at Colorado, with more than $1.3 billion dollars of weed sold last year, with about half the population of just LA county. Jobs, tax money, revenue! These are the things that usually make a politician go to sleep with a smile on his face.

But that doesn’t mean Mark Ridley-Thomas — chair of the Board of Supervisors in Los Angeles County — has to like it. As a matter of fact, as the self-described “card-carrying progressive” declares in an op-ed published in the Los Angeles Times this week, he’s not sure if he likes it at all:

“It is the will of the voters, yet I remain concerned about the impact that recreational/non-medical cannabis commerce could have on the health and safety of neighborhoods throughout Los Angeles County.”

What’s giving him pause? Among other classic canards, he dusts off the good old gateway theory.

In justifying why he’s reluctant to end the illicit market and start capturing tax revenue, Ridley-Thomas gives a rundown of every cherry-picked statistic that anti-legalization zealots trot out whenever anyone makes the mistake of asking; six percent of pregnant women in Colorado reported using marijuana, five percent of high school students say they smoke weed every day, traffic fatalities where marijuana was present are on the rise.

Left unsaid are the inconvenient facts that, in the age of marijuana legalization, teen use of all drugs is at an all-time low, according to the National Institutes on Drug Abuse, and that there’s not yet been any nexus between marijuana detected in a fatal crash and marijuana intoxication, since weed metabolites are found in the body long after the psychoactive effects have worn off.

But according to Ridley-Thomas, “the Los Angeles County Department of Public Health has found that early and regular marijuana use is associated with use of other illicit drugs, including cocaine, hallucinogens, prescription opioids and heroin.”

But does it? Ridley-Thomas doesn’t identify the finding in question. A web search of the LA DPH’s reports does turn up a 2015 presentation, in which the county’s interim health director declares that “it is undeniable that the commercialization of marijuana and marijuana products could have detrimental effects on the health, safety, and well-being of our communities.”

Cities and counties don’t have the resources to conduct their own studies. Such facts, whenever they are posited, come from researchers. In America, the top authority on substance abuse is the federal government’s NIDA.

But, as NIDA reports on its website, “the majority of people who use marijuana do not go on to use other, ‘harder substances.’”

A far more accurate indicator of drug-seeking patterns are “social conditions,” like poverty, a broken home, abuse and/or trauma. As it happens, adolescents who smoke cigarettes and drink alcohol are also likely to lead to other substances.

“Daily use of any substance, including marijuana, places individuals at high risk for addiction,” Samuel Ball, president and CEO of the National Center on Addiction and Substance Abuse, told CNN.

In short, there’s nothing about cannabis that poses a unique risk to anyone.

In any case, NIDA declares that gateway theory is just that — a theory — and far from established science. But, since politicians’ op-eds are not peer-reviewed studies, junk science and bunk arguments get printed.

Gateway theory isn’t even the worst of it.

“Let’s be clear that gangs and cartels operate outside regulation, and dismantling this illegal market operating within saturated communities will be daunting,” Ridley-Thomas continued.

This is the most disingenuous statement of all — and the clearest argument yet for a regulated, legal marketplace. A market cannot exist if there is no demand. There is demand for black-market marijuana only if there’s no legal alternative.

Most everyone not in elected office, in law enforcement, or in the pharmaceutical industry is able to see this, one of the simplest of economic theories — Vicente Fox, the former president of Mexico, sees it.

So what’s up with Mark Ridley-Thomas?

Running for supervisor in LA requires a fair bit of money. According to campaign finance disclosure forms, Ridley-Thomas is bankrolled mostly by LA-area entertainment executives, attorneys, real-estate investors, and other respectable professionals. But he also receives money from organized labor, including law-enforcement interests like the probation officers’ union. That could explain why he’s working so hard to find any reason at all, no matter how spurious, to slow down the legalization train.

But marijuana money has also helped Ridley-Thomas get elected. His official campaign committee took contributions from the United Food and Commercial Workers, the labor union working to organize cannabis dispensaries. And a PAC that supports the politician accepted more than $12,000 from Ghost Group, the venture-capital firm set up by Justin Hartfield, co-founder of Weedmaps, the “Yelp for marijuana” and one of the biggest names in corporate cannabis.

On the one hand, it could be see as a sign of independence that Ridley-Thomas will accept contributions from sources involved in the marijuana industry before dumping all over it. On the other, it would be nice if he could bother to find a legitimate argument when doing it.